Patent GB-312096-A (GB)
Title: Improvements in or relating to the manufacture of cellulose esters
IPC: C08B3/02
Filed: 1927-12-17
Abstract: 312,096. Dreyfus, H. Dec. 17, 1927. Cellulose carboxylates.-Cellulose acetates and cellulose esters of higher homologues of acetic acid are prepared by esterifying cellulosic materials by means of fatty acid anhydrides, particularly acetic anhydride, in presence of a condensing agent comprising stannic chloride or other stannic halide or mixtures thereof, with or without hydrochloric or other hydrohalide acid or mixtures thereof. These catalysts may also be used in conjunction with halides, particularly chlorides, of iron, particularly ferric, manganese, copper, nickel, or cobalt. The best results are obtained when stannic chloride is present in proportions of 7-25 per cent on the weight of cellulose, while if hydrochloric acid is employed together with stannic chloride, both are preferably present in the proportion of 5-15 per cent. As initial materials, there may be employed fibres, fabrics or the like, for example cotton or other celluloses or near conversion products thereof or alternatively viscose silk or other regenerated cellulosic artificial fibres. Wood pulps, bamboo or esparto or other materials containing encrusting matter from which the lignin, pemtosan, resin and like consituents have been substantially removed as in sulphite pulp, soda pulp or sulphate pulp may be employed but chemical pulps are preferably subjected to an alkaline purifying treatment as described in Specification 249,173. Partially esterified or etherified products may also be esterified in this manner. The cellulosic materials may be subjected to a pretreatment with organic acids in any suitable manner such as with concentrated or dilute acids particularly lower aliphatic acids such as formic and acetic acids, in order to increase their reactivity. The pretreatment with organic acids may be carried out, for example, with formic acid, preferably of 80-100 per cent strength, or acetic acid, or with the vapours of these acids as described in Specification 263,938. After the treatment with organic acids, the cellulosic materials may be subjected to a stream of air or inert gas or to suction or vacuum to remove the organic acids wholly or partially. When stannic chloride or other halide is employed in the subsequent esterification in absence of hydrohalide, acid. the cellulosic materials should be so pretreated with organic acids. In order to avoid degradation of the celulose molecule, the esterification should be conducted at temperatures not exceeding 50‹ C. and may be conducted at 0‹ C. or even lower. The hydrohalide acid may be applied in any suitable, form, either in solution or as a gas, and may be introduced after the reaction has been started with stannic chloride or other halide salt for instance it may be added all at once or in portions at intervals or continuously during the reaction but preferably the combined catalysts are added to the esterifying mixture before addition of the cellulose or alternatively to the cellulose before adding the anhydride. The stannic chloride or other halide salt may be incorporated in the cellulosic materials prior to the acetylation or esterification. Esterification may be performed in presence of a solvent for the cellulose ester particularly acetic acid, the quantity of the solvent being for example from 4 to 6 times the weight of the cellulosic material but esters of especially high viscosity can be prepared when the solvent is present in a quantity for example equal to from 8 to 20 times or more the weight of the cellulosic material, as described in Specification 207,562. Small quantities e.g. 0.5 to 10 per cent of more powerful organic solvents such for example as ethylidene diaoetate, lactic acid, or its acetyl derivatives may be added to the acetic acid or other solvent as indicated in Specification 263,939 or may be produced in solution, for example by addition of acetaldehyde to produce ethylidene diacetate by reaction with the acetic anhydride. Alternatively the esterification may be conducted in suspension in liquid non-solvents, for example benzene or toluene, as described in Specification 20979/11, or in mixtures thereof with solvents, such as acetic acid, but in the latter case, the non-solvent should be present in sufficient quantity to prevent solution of the cellulose ester. The esterification may be further performed substantially in absence of liquid solvents or non-solvents by employing the vapours of acetic anhydride or other esterifying agent as described in Specification 264,937. In examples, cotton linters are pretreated with formic acid of 75-100 per cent strength, washed for example with water or benzol centrifuged or dried and introduced into a mixture of acetic anhydride, glacial acetic acid, stannic chloride, and hydrochloric acid at atmospheric temperature with constant stirring until a clear solution of cellulose acetate is obtained; linters pretreated as above are acetylated in the cold in a mixture of acetic anhydride, glacial acetic acid, and stannic chloride; cotton linters are heated with glacial acetic acid and then cooled, whereupon stannic chloride and acetic acid are added followed by benzene mixed with acetic anhydride for esterification; cotton linters are esterified in the cold in a mixture of glacial acetic acid. acetic anhydride, stannic chloride, and hydrochloric acid. The cellulose esters obtained may be subjected to secondary treatments either in the primary esterification solutions or suspensions, preferably without neutralizing the hydrohalide acid or removing the stannic halide present and after destroying any remaining anhydride with water or other agents, such as hydroxyl derivatives, oxy acids such as lactic acid, alcohols, &c. If no acid is used in the esterification, hydrochloric or other hydrohalide acid may be added to accelerate the reaction. Alternatively the esters, either precipitated from the primary solutions or those obtained other than in solutions, may be dissolved or suspended and then subjected to the secondary treatments. Inorganic or organic acids, acid salts or other suitable agents may be added, the treatment being stopped when the desired solubility has been reached. It is particularly advantageous to conduct the further treatments in the presence of hydrochloric acid and stannic chloride or other catalysts used according to the present invention. The secondary treatments may be conducted at ordinary temperatures or at temperatures up to 80‹ C.- 100‹ C. but in the latter case, the presence of free mineral acid is preferably to be avoided. To obtain acetone solubility, it is in general unnecessary to carry the secondary treatments so far as hitherto and consequently the acidyl content of the acetone-soluble esters may be higher. Cellulose esters soluble in acetone or very low boiling solvents, such as methyl formate, acetaldehyde, formaldehyde, &c. may be prepared by these processes and high boiling solvents, plasticizing agents, or softemog agents can readily be incorporated with them or with their solutions in volatile solvents. The esters may be employed for the production of artificial silk, films, celluloid substitutes or other thermoplastic masses, moulding powders, &c. either in their primary esterification solutions or as primary or secondary esters in solution in suitable solvents, for example acetone, ethyl alcoholacetone, methyl alcohol-acetone, or the low boiling point solvents already referred to or in mixtures of such solvents. For wet or dry spinning processes, the esters may be employed in solutions containing 5-30 per cent or more of the ester. Artificial silks &c. prepared from the secondary esters are much more resistant to delustring by boiling or hot aqueous solutions or moist steam and may even resist delustring altogether. Suitable precipitating liquids for use in wet spinning comprise alcohols for example methyl or ethyl alcohols or their homologues, coal tar, petroleum or other hydrocarbons, for instance benzene, toluene, and their homologues, gasoline, or kerosene, and aqueous liquids containing mineral acids for example sulphuric acid. and acid salts, for example bisulphates, neutral salts for example sodium, potassium, calcium, or magnesium chloride, or substances which have a latent solvent power for the cellulose esters for example thiocyanates. zinc chloride, acetone, diacetone alcohol, alcohol, acetic acid or formic acid or other salts as described in Specifications 177,868 and 179,234. Such precipitant liquids may also be incorporated in the spinning solutions prior to extrusion. Apparatus for dry spinning may be of the type described in Specifications 165,519, 198,023, 203,092, 300,998, and 304,674. For wet spinning any suitable apparatus may be used, for example apparatus of the type employed in the spinning of viscose, cuprammonium. or nitro-cellulose artificial silks. Specification 312,098 also is referred to.